The role of the solitary and paramedian reticular nuclei in mediating cardiovascular reflex responses from carotid baro- and chemoreceptors

1. With dye-filled micro-electrodes single neurones in the medulla of anaesthetized paralysed cats were identified which: (a) fired rhythmically in synchrony with or were modulated by the cardiac cycle, and which ceased firing with occlusion of the ipsilateral common carotid artery (carotid sinus baroreceptor neurones); (b) were excited by stimulation of carotid body chemoreceptors by close intra-arterial injection of lobeline into the thyroid artery (carotid body chemoreceptor neurones).2. Twelve carotid baroreceptor neurones were identified, in thirty-three cats, nine of which were localized in the intermediate area of the nucleus of the solitary tract (NTS) within 1 mm ahead of or behind the obex; three units were located either in the parahypoglossal area or the dorsal portion of the paramedian reticular nucleus (PRN).3. Of the twenty-one carotid chemoreceptor neurones which were identified, thirteen were localized in the NTS, three in the parahypoglossal area and four in the dorsal PRN.4. Bilateral lesions of the paramedian reticular area of medulla destroying the PRN, abolished or reversed the depressor response to electrical stimulation of myelinated fibres of the carotid sinus nerve (CSN), attenuated the depressor response to carotid sinus stretch and augmented the pressor response to chemoreceptor stimulation by lobeline. Such lesions did not significantly alter the reflex heart rate responses.5. Small lesions of the NTS within an area 1 mm rostral to the obex abolished all reflex blood pressure and heart rate responses to electrical stimulation of the CSN or natural stimulation of carotid baro- or chemoreceptors.6. Baroreceptors and chemoreceptors of the CSN project both to the intermediate zone of the NTS and to more medial areas of the medulla, particularly the dorsal PRN and parahypoglossal area.7. The PRN serves to mediate the reflex depressor, but not cardio-vagal, response from myelinated baroreceptors and buffers the pressor responses from chemoreceptors; it may serve as an important area integrating cardiovascular activity descending from forebrain, brain stem and cerebellum with baroreceptor reflexes.8. Cardiovascular reflex responses arising from non-myelinated baroreceptors and all chemoreceptors are mediated by neurones in the intermediate area of the NTS.     

Vestibular and optokinetic eye movements evoked in the cat by rotation about a tilted axis

Summary Horizontal and vertical eye movements were recorded from cats in response to either a) off-vertical axis rotation (OVAR) at a range of velocities (5–72 deg/s) and a range of tilts (0–60 deg) or b) horizontal (with respect to the cat) optokinetic stimulation (10–80 deg/s), also around a range of tilted axes (0–60 deg). The responses to stopping either of these stimuli were also measured: post-rotatory nystagmus (PRN) following actual rotation, and optokinetic after nystagmus (OKAN) following optokinetic stimulation. The response found during OVAR was a nystagmus with a bias slow-phase velocity that was sinusoidally modulated. The bias was dependent on the tilt and reached 50% of its maximum velocity (maximum was 73±23% of the table velocity) at a tilt of 16 deg. The phase of modulation in horizontal eye velocity bore no consistent relation to the angular rotation. The amplitude of this modulation was roughly correlated with the bias with a slope of 0.13 (deg/s) modulation/(deg/s) bias velocity. There was also a low-velocity vertical bias with the slow-phases upwardly directed. The vertical bias was also modulated and the amplitude depended on the bias velocity (0.27 (deg/s) modulation/ (deg/s) bias velocity). When separated from the canal dependent response, the build up of the OVAR response had a time constant of 5.0±0.8 s. Following OVAR there was no decline in the time constant of PRN which remained at the value measured during earth-vertical axis rotation (EVAR) (6.3±2 s). The peak amplitude of PRN was reduced, dependent on the tilt, reaching only 20% of its EVAR value for a tilt of 20 deg. When a measurable PRN was found, it was accompanied by a slowly-emerging vertical component (time constant 5.4±2s) the effect of which was to vector the PRN accurately onto the earth horizontal. OKN measured about a tilted axis showed no differences in magnitude or direction from EVAR OKN even for tilts as large as 60 deg. OKAN following optokinetic stimulation around a tilted axis appeared normal in the horizontal plane (with respect to the animal) but was accompanied by a slowly emerging (time constant 4.1±2 s) vertical component, the effect of which was to vector the overall OKAN response onto the earth horizontal for tilts less than 20 deg. These results are compared with data from monkey and man and discussed in terms of the involvement of the velocity storage mechanism.     

Inhibition of the responses of cat dorsal horn neurons to noxious skin heating by stimulation in medial or lateral medullary reticular formation

Summary Responses of single lumbar dorsal horn units to noxious radiant heating (50° C, 10 s) of glabrous footpad skin were recorded in cats anesthetized with sodium pentobarbital and 70% nitrous oxide. The heat-evoked responses of 37/40 units were reduced during electrical stimulation (100 ms trains, 100 Hz, 3/s, 25–600 A) in the medullary nucleus raphe magnus (NRM) and/or in laterally adjacent regions of the medullary reticular formation (MRF). Inhibition was elicited by stimulation in widespread areas of the medulla, but with greatest efficacy at ventrolateral sites. The magnitude of inhibition increased with graded increases in medullary stimulation intensity. Mean current intensities at threshold for inhibition or to produce 50% inhibition were higher for NRM than for MRF sites. Units' responses to graded noxious heat stimuli increased linearly from threshold (42–43° C) to 52° C. During NRM (5 units) or ipsilateral MRF stimulation (7 units), responses were inhibited such that the mean temperature-response functions were shifted toward higher temperatures with increased thresholds (1.5° and 1° C, respectively) and reduced slopes (to 60% of control). Contralateral MRF stimulation had a similar effect in 4 units. Inhibitory effects of NRM and MRF stimulation were reduced (by >25%) or abolished in 4/6 and 5/12 units, respectively, following systemic administration of the serotonin antagonist methysergide. Inhibitory effects from NRM, ipsi- and contralateral MRF were reduced or abolished in 2/9, 4/8 and 6/9 cases, respectively, following systemic administration of the noradrenergic antagonist phentolamine. These results confirm and extend previous studies of medullospinal inhibition and the role of monoamines, and are discussed in terms of analgesic mechanisms.     

Effect of Temperature on Guinea Pig Urinary Bladder Contraction Mediated via P2X-Receptors

In vitro experiments showed that P2X-receptor agonist ,-methylene-ATP and electrical field stimulation in the presence of muscarinic and -adrenoreceptors blockers induced contractile responses of isolated guinea pig bladder, which were more pronounced at 30°C than at 37°C or 42°C. P2X-receptor antagonist pyridoxal-6-phosphate-2',4'-disulfonic acid, produced a more potent inhibitory effect on contractions induced by electrical field stimulation at 30°C in comparison with that at 37°C or 42°C, while the contractions induced by ,-methylene-ATP were similarly suppressed at all examined temperatures.     

Activation of the parapyramidal region in the ventral medulla stimulates gastric acid secretion through vagal pathways in rats

Neurons synthesizing thyrotropin-releasing hormone, substance P and serotonin in the medullary caudal raphe nuclei project to the dorsal vagal complex and play a role in the central vagal regulation of gastric function. Neurons in the parapyramidal region in the ventral medulla share similar biochemical coding and projections as those in the caudal raphe nuclei. The role of the parapyramidal region in the autonomic regulation of gastric acid secretion was investigated in urethane-anesthetized rats. Unilateral microinjection of kainate into the parapyramidal region at 10, 15 and 20 ng induced a dose-related stimulation of gastric acid secretion (net increases: 22.2±11.2, 40.5±8.5 and 89.8±19.4 μmol/60 min, respectively), while injection of vehicle had no effect (net change: −0.1±1.4 μmol/60 min). Time-course studies showed a nine-fold peak increase over basal at 30 min after parapyramidal injection of kainate (20 ng) and acid secretion returned to basal level at 70 min. Microinjections of kainate (15–20 ng) outside the parapyramidal region or into the parapyramidal region in vagotomized rats had no effect. Exposure to cold (4°C) for 2 h, which is known to induce vagally mediated gastric secretory and motor responses through medullary thyrotropin-releasing hormone pathways, increased the number of Fos-positive cells in the caudal, middle and rostral parts of the parapyramidal region to 4.3±0.4, 9.4±0.9 and 18.4±1.6/section, respectively, compared with 0.1±0.1, 0.1±0.0 and 0.7±0.6/section, respectively, in rats maintained at room temperature. Most of the Fos-labeled cells co-expressed pro-thyrotropin-releasing hormone messenger RNA signal and/or were serotonin immunoreactive.These data show that chemical activation of neurons in the parapyramidal region results in a vagal-dependent stimulation of gastric acid secretion and that acute cold exposure activates parapyramidal neurons containing pro-thyrotropin-releasing hormone and/or serotonin, suggesting a potential role of the parapyramidal region, in addition to the caudal raphe nuclei, as medullary sites involved in the vagal regulation of gastric function.     

Hypothermia-induced potentiation of histamine H2-receptor-mediated relaxation and cyclic AMP increase in the isolated mesenteric artery of the rabbit

On helically cut strips of the rabbit's mesenteric artery, a temperature decrease from 42°C to 25°C reduced the contractile responses to histamine. Metiamide shifted the dose-response curve of the histamine-induced contraction towards higher values at 25°C, but not at 42°C. Furthermore, on arterial strips contracted by phenylephrine histamine evoked a dose-dependent relaxation at 25°C whereas at 42°C only slight relaxing responses to histamine occurred. Metiamide was capable of preventing the relaxation induced by histamine in a competitive manner.At 25°C the relaxation as produced by histamine was accompanied by increases in cyclic AMP which occurred prior to the relaxing effects. Metiamide abolished the cyclic AMP increase in response to histamine. At 42°C histamine was unable to elevate the cyclic AMP content.Thus, it is concluded that a cyclic AMP-mediated relexation due to stimulation of H₂-receptors counteracts the histamine-induced contraction and reduces the contractile responses to histamine at low temperatures. In addition, clear-cut evidence exists from the present study that also on artery smooth muscle the H₂-receptor-mediated responses are closely associated to cyclic AMP.     

Phase-dependent reversal of reflexly induced movements during human gait

Summary To investigate whether phase-dependent reversals in reflex responses on electromyography (EMG) are accompanied by movement reversals, a series of human volunteers were studied for their behavioural responses to sural nerve stimulation during running or walking on a treadmill. Low-intensity stimulation (< 2.5 x perception threshold, T) of the sural nerve yielded facilitatory responses in the tibialis anterior muscle (TA), correlated with an induced ankle dorsiflexion (mean maximum 4°) in early swing. The same stimuli yielded primarily TA suppression and weak ankle plantar flexion (mean maximum 1°) at end swing. The correlated induced knee angle changes did not precede the ankle changes, and they were relatively small. Mean maximum flexion in early swing was 6.2°, while mean maximum extension was 3.7°. High-intensity stimulation of the sural nerve (> 2.5 x T) always gave rise to suppression of the ongoing activity. This resulted in a second type of movement reversal. During late stance and early swing the responses in TA were suppressive (i.e. below background activity) and related to ankle plantar flexion. In contrast, the responses during early and middle stance consisted of suppression in extensor activity (gastrocnemius medialis and soleus) and ankle dorsiflexion.The data are discussed in terms of a new hypothesis, which states that the responses to electrical stimulation of cutaneous nerves during locomotion do not correspond directly to corrections for stumbling following mechanical perturbations during the step cycle. Instead, the data invite a reinterpretation in terms of the opening and closing of reflex pathways, presumably by a central pattern generator for locomotion.     

An effect of the electrogenic sodium pump on the membrane potential in beating guinea-pig atria

Summary The membrane potential of guinea-pig atria was measured in different media before, during and after electrical stimulation of various durations. The stimulus duration and frequency (3 pulses/sec) were kept constant.During short stimulation (<1 min) in Tyrode solution at 35°C the membrane potential depolarized first quickly and later on more slowly. Following cessation of the stimulus train the membrane potential repolarized to the resting value within 1–2 min.Prolonged stimulation (1–7 min) in Tyrode solution at 35°C likewise caused an initial depolarization of membrane potential. Thereafter, the membrane potential repolarized although stimulation continued. After the end of the stimulation period the membrane potential hyperpolarized beyond the resting potential for several minutes. Maximum hyperpolarization was achieved ca. 1 min after the end of the stimulus train.In Tyrode solution at 25°C both the repolarization of the membrane potential during long stimulation and the hyperpolarization after it were diminished. The same effect was observed in Na poor fluids, which contained only 50 or 33% of the Na concentrations in Tyrode solution.Digitoxigenine (3·10^–6 g/ml), when added to Tyrode solution at 35°C, also reduced the repolarization of membrane potential during, and the hyperpolarization after, a long stimulus train.Compared to the resting value the membrane resistance was essentially unchanged 1–3 min after a 2 min stimulation period.From these results it is concluded, that an active, electrogenic Na pump contributes to the membrane potential of beating guinea-pig auricles.     

The central pattern generator for vomiting may exist in the reticular area dorsomedial to the retrofacial nucleus in dogs

There is some controversy over whether or not a discrete site that integrates vomiting activities in somatic and autonomic nerves is present in the medulla oblongata. On the basis of our previous studies, we hypothesized that the temporal patterns of muscle contractions in vomiting are generated by a central pattern generator in the retrofacial area of the rostral medulla. To investigate this hypothesis further, the effects of electrical and chemical lesions of the medullary area were observed in decerebrate paralyzed dogs. Efferent activities of the phrenic and abdominal muscle nerves were recorded to recognize fictive vomiting. The right half of the medulla oblongata was transversely severed about 3 mm rostral to the obex. Fictive vomiting responses to vagal stimulation still appeared after hemisection in all 11 dogs. In addition, stimulation of the contralateral reticular area dorsomedial to the retrofacial nucleus produced fictive vomiting even after hemisection. An electrical lesion or injection of kainic acid (0.5–1.0 μl) was applied at the point where reticular stimulation induced fictive vomiting. After this destruction, no activities that corresponded to fictive vomiting could be induced by stimulation of vagal afferents or the reticular site. Salivation was decreased by hemisection, and decreased further, but was not completely abolished, with destruction of the reticular area. Kainic acid is known to selectively destroy neural cell bodies. Therefore, we concluded that neuronal somata in the reticular formation dorsomedial to the retrofacial nucleus play an essential role in the central patterning of vomiting activities in peripheral motor nerves. Received: 10 September 1996 / Accepted: 2 July 1997     

Evaluation of hypothalamic thermosensitivity by feedback signals

Summary In four conscious goats with chronically implanted hypothalamic thermodes, forty-three experiments were carried out at environmental conditions between +5°C and 30°C DB/18°C WB. The temperature of the hypothalamus was altered by perfusing the thermodes with water whose temperature, as measured at the inlet of the thermodes, varied between 30°C and 43°C. Heat production, respiratory evaporative heat loss, rectal and oesophageal temperatures were measured. Hypothalamic cooling resulted in an elevation of rectal temperature, while hypothalamic heating caused a fall in temperature. The relation between the intensity of hypothalamic thermal stimulation and the induced change in core temperature can be well described by linear regressions. No difference in sensitivity and no dead band between responses to cold and warm stimulation was found. The experiments show that hypothalamic and extra-hypothalamic sensors of core temperature continuously operate at high sensitivity even within the narrow range of physiologically occurring core temperatures. Qualitatively, this sensitivity is independent of air temperatures between +5°C and +30°C.     

Stimulation of a bulbospinal 5-HT pathway in the rat brain produces hyperglycaemia

The glucoregulatory role of spinally projecting serotonin (5-HT) neurones near the ventrolateral surface of the medulla oblongata was investigated by stimulating these nerve cells in normal rats and in rats with selective chemical ablation of 5-HT nerves in the spinal cord. Electrical stimulation of the lateral medulla produced hyperglycaemia in normal rats; the increase in blood glucose was proportional to the intensity and frequency of stimulation. Furthermore, microinjection of kainic acid or L-glutamate at the same sites also produced hyperglycaemia. This stimulation-induced hyperglycaemia was significantly reduced by spinal transection or adrenalectomy. Selective destruction of spinal 5-HT nerves produced by intraspinal injection of 5,7-dihydroxytryptamine also reduced the magnitude of the hyperglycaemia response to electrical stimulation of the lateral medulla. This indicates that stimulation of 5-HT nerve cells adjacent to the ventrolateral surface of the medulla oblongata and projecting to the spinal cord increases the adrenal-sympathetic efferent activity and leads to hyperglycaemia in rats.     

L-dopaergic components in the caudal ventrolateral medulla in baroreflex neurotransmission.

L-3,4-Dihydroxyphenylalanine (L-DOPA) is probably a transmitter of the primary baroreceptor afferents terminating in the nucleus tractus solitarii; L-DOPA functions tonically to activate depressor sites of the caudal ventrolateral medulla, which receives input from the nucleus tractus solitarii [Misu Y. et al. (1996) Prog. Neurobiol. 49, 415-454]. We have attempted to clarify whether or not L-DOPAergic components within the caudal ventrolateral medulla are involved in baroreflex neurotransmission in anesthetized rats. Electrolytic lesions of the right nucleus tractus solitarii (1 mA d.c. for 10 s, 10 days before measurement) selectively decreased by 45% the tissue content of L-DOPA in the dissected ipsilateral caudal ventrolateral medulla. Electrolytic lesions did not decrease dopamine, norepinephrine and epinephrine levels. During microdialysis of the right caudal ventrolateral medulla, extracellular levels of L-DOPA, norepinephrine, epinephrine and 3,4-dihydroxyphenylacetic acid were consistently detectable using high-performance liquid chromatography with electrochemical detection. However, extracellular dopamine levels were lower than the assay limit. Baroreceptor activation by i.v. phenylephrine selectively evoked L-DOPA without increasing the levels of norepinephrine, epinephrine and 3,4-dihydroxyphenylacetic acid. This L-DOPA release was suppressed by acute lesion in the ipsilateral nucleus tractus solitarii. Intermittent stimulation of the right aortic depressor nerve (20 Hz, 3 V, 0.3 ms duration, for 30 min) repetitively and constantly caused L-DOPA release, hypotension and bradycardia, without increases in levels of norepinephrine, epinephrine and 3,4-dihydroxyphenylacetic acid. Local inhibition of L-DOPA synthesis with alpha-methyl-p-tyrosine (30 microM) infused into the ipsilateral caudal ventrolateral medulla gradually decreased basal levels of L-DOPA and 3,4-dihydroxyphenylacetic acid without decreasing norepinephrine and epinephrine. The inhibition of L-DOPA synthesis interrupted L-DOPA release and decreased by 65% depressor responses elicited by aortic nerve stimulation; however, it produced no effect on bradycardic responses. CoCl2 (119 ng), a mainly presynaptic inhibitory transmission marker, and L-DOPA methyl ester (1 microg), a competitive L-DOPA antagonist, when microinjected into depressor sites of the right caudal ventrolateral medulla, reduced by 60% depressor responses to transient ipsilateral stimulation of the aortic nerve (20 Hz, 3 V, 0.1 ms duration, for 10 s). No changes in bradycardic responses were observed. There may exist an L-DOPAergic relay from the nucleus tractus solitarii to the caudal ventrolateral medulla. L-DOPAergic components in the caudal ventrolateral medulla are involved in baroreflex neurotransmission via a baroreceptor-aortic depressor nerve-nucleus tractus solitarii-caudal ventrolateral medulla relay in the rat.     

Activation of the parapyramidal region in the ventral medulla stimulates gastric acid secretion through vagal pathways in rats

Neurons synthesizing thyrotropin-releasing hormone, substance P and serotonin in the medullary caudal raphe nuclei project to the dorsal vagal complex and play a role in the central vagal regulation of gastric function. Neurons in the parapyramidal region in the ventral medulla share similar biochemical coding and projections as those in the caudal raphe nuclei. The role of the parapyramidal region in the autonomic regulation of gastric acid secretion was investigated in urethane-anesthetized rats. Unilateral microinjection of kainate into the parapyramidal region at 10, 15 and 20 ng induced a dose-related stimulation of gastric acid secretion (net increases: 22.2+/-11.2, 40.5+/-8.5 and 89.8+/-19.4 micromol/60 min, respectively), while injection of vehicle had no effect (net change: -0.1+/-1.4 micromol/60 min). Time-course studies showed a nine-fold peak increase over basal at 30 min after parapyramidal injection of kainate (20 ng) and acid secretion returned to basal level at 70 min. Microinjections of kainate (15-20 ng) outside the parapyramidal region or into the parapyramidal region in vagotomized rats had no effect. Exposure to cold (4 degrees C) for 2 h, which is known to induce vagally mediated gastric secretory and motor responses through medullary thyrotropin-releasing hormone pathways, increased the number of Fos-positive cells in the caudal, middle and rostral parts of the parapyramidal region to 4.3+/-0.4, 9.4+/-0.9 and 18.4+/-1.6/section, respectively, compared with 0.1+/-0. 1, 0.1+/-0.0 and 0.7+/-0.6/section, respectively, in rats maintained at room temperature. Most of the Fos-labeled cells co-expressed pro-thyrotropin-releasing hormone messenger RNA signal and/or were serotonin immunoreactive. These data show that chemical activation of neurons in the parapyramidal region results in a vagal-dependent stimulation of gastric acid secretion and that acute cold exposure activates parapyramidal neurons containing pro-thyrotropin-releasing hormone and/or serotonin, suggesting a potential role of the parapyramidal region, in addition to the caudal raphe nuclei, as medullary sites involved in the vagal regulation of gastric function.     

Salivary cooling,escape reaction and heat pain in capsaicin-desensitized rats

Salivary thermolytic mechanism (weight of salivary glands, effect of desalivation on water intake and body temperature, grooming activity) as well as escape behaviour and reaction to heat pain were studied in capsaicin-desensitized and control rats exposed to various warm ambient temperatures. Body temperature of the desensitized rats increased more than the controls at all the ambient temperatures studied (32, 34 and 36°C); however, significant differences in the mechanism of salivary cooling were obtained only at 34 and 36°C. Central impairment of saliva spreading in desensitized rats seems evident. Complete surgical desalivation did not increase hyperthermia of control and desensitized animals in warm environments. Therefore other mechanisms, primarily vasodilatatory, must also be involved in the rat's thermolytic normal response. Although desensitized rats did not show a tendency to escape from the warm environment their response to heat pain was normal. In conclusion, it is suggested that heat perception in desensitized animals is impaired; however, the existence of some capsaicin-insensitive thermolytic mechanisms (prone extension of the body) cannot be excluded.Supported by the Scientific Research Council, Ministry of Health, Hungary /4-05-0303-04-2/0/ and MTA-OM-MÉM-EÜM 70.211/79     

Physiological and subjective responses to thermal transients of exercising subjects dressed in cold-protective clothing

In cold conditions variations in the physical activity of clothed individuals and rest periods in a moderate temperature may result in a disturbance of heat balance and thermal comfort of the individual, in particular when sweating occurs. The purpose of the study was to examine thermal responses in persons dressed in winter clothing during changes of exercise intensity (high to low) and ambient temperature, and to investigate whether there were any effects on these responses due to fibre material (wool and synthetic). Two types of transient condition were studied, an exercise level transient (E) and a temperature transient (T). Ten healthy male subjects dressed in multi-layer winter clothing ensembles with different levels of total insulation walked on a treadmill at an ambient temperature of – 10°C. The garments were manufactured from wool, giving insulations of 2.6 clo, in T only and otherwise of 3.2 clo, or synthetic fibres, giving insulations of 2.4 clo in T only and otherwise of 3.1 clo. In E the subjects exercised at a high intensity for 50 min followed by 60 min walking at low intensity. In T they walked at a moderate speed for 90 min in ambient temperature of – 10°C, rested in temperatures of + 22°C for 30 min and walked in the cold climatic chamber for another 45 min. The skin temperature, sweating responses and thermal sensations were higher/warmer with increasing insulation during exercise. The wool fibre material resulted in a slightly higher mean skin temperature (about 0.3°C) during exercise, but no differences in subjective responses were found. The rest period had only a small influence on the subsequent thermal responses. The interindividual variations in thermal responses were large.     

Respiratory effects on high cervical cord cold blockade on efferent vagal and phrenic discharges in the rabbit

A technique of reversible cold blockade was applied in decerebrate and vagotomized rabbits that were immobilized and artificially ventilated to study the modulation of spontaneous respiratory rhythms. Respiratory discharges were recorded from vagal and phrenic efferents before and during cold blockade at the second cervical segment (C2) with a coolant-circulated thermode (–15° C). Measurement of the cooling profile demonstrated that there was significant hypothermia in the regions of the phrenic nucleus (+25° C) and obex of the medulla (+26° C). Arterial pressure was maintained by continual norepinephrine infusion, end-tidal carbon dioxide tension was held at hypercapnic levels, and rectal temperature was regulated near 38°C. The cold blockade of descending respiratory drives to the cervical phrenic nucleus inhibited the spontaneous activity in the phrenic nerve for more than 90 min. Phrenic activity could be induced by the intravenous injection of strychnine, but not doxapram, although this was not of respiratory quality. These results show that in the absence of descending and pharmacologic drives, but in the presence of phrenic hypothermia, spinalized rabbits are incapable of generating rhythmic patterns of discharge. C2 cold blockade also significantly slowed the spontaneous central respiratory rhythm with no change in integrated vagal amplitude, presumably due to a direct cooling effect on brainstem oscillators for breathing.     

Transient cold pain has no effect on cutaneous vasodilatation induced by capsaicin: a randomized-control-crossover study in healthy subjects

Cooling the skin induces sympathetically driven vasoconstriction, along with some vasoparalytic dilatation at lowermost temperatures. Neurogenic inflammation, on the other hand, entails vasodilatation. In the present study, we examined the dynamic vasomotor balance of capsaicin-induced vasodilatation within the area of the induced neurogenic inflammation, with and without superimposed cooling. In a randomized-control-crossover fashion, a sample of 14 healthy volunteers participated in three experiments: (1) exposure to each 0°C cold pain stimulus and a neutral 30°C stimulus (control) for 30 s to the volar forearms by contact thermal thermode (1.6×1.6 cm²), (2) injection of 50 μg intradermal capsaicin without cooling and (3) injection of capsaicin followed by application of 0°C cold pain stimulation for 30 s within the area of the secondary hyperalgesia. Repetitive vascular measurements over skin area of 4.0×4.0 cm² of blood flux (BF) were acquired before and during the 5 min after stimulation. A marked increase in BF (i.e. vasodilatation) at the location of the cold stimulus in comparison to control (30°C) (F=11.97, p=0.004) within the first 3 min was demonstrated. Two-way repeated-measures ANOVA indicated no interaction between the experimental conditions (capsaicin with or without cold) and time (F=0.934, p=0.454). The cold pain stimulation was found to be insignificant in its influence on BF evoked by capsaicin (F=0.018, p=0.894). The results of our study indicate that (1) transient cooling causes significant vasodilatation, (2) intradermal injection of capsaicin is dominant in inducing vasodilatation, and (3) the cold-pain-evoked vasodilatation has no modulative effect on the capsaicin-evoked cutaneous vasodilatation.     

Impulse activity of medulla oblongata in rats in response to stimulation of taste receptors and visceral chemoreceptors

We have recorded extracellularly the impulse activity of the rat medulla oblongata during stimulation of taste receptors of the tongue and visceral chemoreceptors with solutions of hydrochloric acid and sodium chloride. We have detected in the caudal region of the nucleus of the solitary tract, neurons that react to the chemical stimulation of either one or both the receptive zones mentioned. The response reactions of the isolated groups of units (taste, viscerochemical, and convergent neurons) are tonic and are characterized by a high level of impulse activity. We have established that the neurons of each of the groups isolated are capable of discriminating between salt and acid solutions. Using the example of sodium chloride solutions we have shown that an increase in the number of viscerochemical neurons which inhibit their own background activity on increase in the concentration of any substance in the intestine is an important index of the satiation of an animal and can serve as a starting link in the mechanism of food rejection.Translated from Fiziologicheskii Zhurnal SSSR imeni I. M. Sechenova, Vol. 68, No. 10, pp. 1337–1343, October, 1982.     

Comparisons of the sensation perceived and intradental nerve activity following temperature changes in human teeth

Summary The relationship between the intradental nerve responses and subjective sensory ratings evoked by thermal stimulation of the teeth was studied in man. Recordings were taken from a total of 12 thermally sensitive units from the inferior dental nerve following thermal tooth stimulation, of which seven responded to both heating and cooling, two were exclusively cold-sensitive and three exclusively heat-sensitive. The early and late sensory responses following both cold and heat stimulation of the tooth were observed. The late sensory responses were more unstable than the early sensory responses. The mean threshold of the early sensory responses to tooth cooling was 13.6±1.9° C (n = 9) and that to heat stimulation was 48.4±4.8° C (n=10). The firing frequency of the heat-sensitive, but not the cold sensitive, units increased linearly in proportion to the increase in magnitude of the early sensory ratings.     

Post-rotatory nystagmus and optokinetic after-nystagmus in the rabbit linear rather than exponential decay

Summary The decay of the slow phase velocity of post-rotatory (PRN) and optokinetic (OKAN) afternystagmus as a function of time was measured in Dutch rabbits after stimulation with velocity steps of 30, 60, and 150 °/s. The decays fitted linear functions very well, but only poorly exponential ones. Typical decay rates were 2–5 °/s², with apparent time constants (defined by decay to 37% of initial velocity) in the order of 10–20 s. Within one animal, the decays of OKAN and PRN with similar initial velocities were indistinguishable. With sinusoidal oscillation, the time constant of the vestibulo-ocular reflex — estimated from phase lead — was only 2–3 s, and probably similar to the cupular time constant. In general, time constants increased when eye velocities increased. This indicates that the vestibulo-ocular reflex of the rabbit behaves as a non-linear system. A velocity storage system with a constant discharge rate is postulated as a main non-linear element. This would introduce a linear decay of velocity as well as a threshold for velocity. This storage system would be common to both vestibulo-ocular and optokinetic reflexes.